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Recent Advances in Reactive Ion Etching and Applications of High-Aspect-Ratio Microfabrication
This paper reviews the recent advances in reaction-ion etching (RIE) for application in high-aspect-ratio microfabrication. High-aspect-ratio etching of materials used in micro- and nanofabrication has become a very important enabling technology particularly for bulk micromachining applications, but increasingly also for mainstream integrated circuit technology such as three-dimensional multi-functional systems integration. The characteristics of traditional RIE allow for high levels of anisotropy compared to competing technologies, which is important in microsystems device fabrication for a number of reasons, primarily because it allows the resultant device dimensions to be more accurately and precisely controlled. This directly leads to a reduction in development costs as well as improved production yields. Nevertheless, traditional RIE was limited to moderate etch depths (e.g., a few microns). More recent developments in newer RIE methods and equipment have enabled considerably deeper etches and higher aspect ratios compared to traditional RIE methods and have revolutionized bulk micromachining technologies. The most widely known of these technologies is called the inductively-coupled plasma (ICP) deep reactive ion etching (DRIE) and this has become a mainstay for development and production of silicon-based micro- and nano-machined devices. This paper will review deep high-aspect-ratio reactive ion etching technologies for silicon, fused silica (quartz), glass, silicon carbide, compound semiconductors and piezoelectric materials.
Journal Article
Phase-shifting cell loaded with variable capacitances for dual linearly polarised reflectarrays
A new dual linearly polarised phase-shifting cell for reflectarray applications is presented. It consists of two orthogonal sets of parallel rectangular slots etched in a ground plane. Each set may be loaded with a combination of variable and fixed capacitances to provide a reconfigurable 2-bit phase-shifter for both polarisations. A passive version of the proposed cell has been fabricated and characterised in C-band with four fixed states. For each polarisation only two variable capacitances are needed in order to control the phase of the reflected wave. [PUBLICATION ABSTRACT]
Journal Article
Rolling Contact Fatigue-Related Microstructural Alterations in Bearing Steels: A Brief Review
Bearings are vital components that are widely used in modern machinery. Although usually manufactured with high-strength steels, bearings still suffer from rolling contact fatigue where unique microstructural alterations take place beneath the contact surface as a result of the complex stress state. Studying these microstructural alterations is a hot research topic with many efforts in recent decades. In this respect, the key information regarding four major types of microstructural alterations, white etching areas/white etching cracks, dark etching regions, white etching bands and light etching regions is reviewed regarding the phenomenology and formation mechanisms. Then, classical and state-of-the-art models are established to predict their formation and are summarised and evaluated. Based on the current research progress, several key questions and paradoxes for each type of microstructural alteration are raised, suggesting possible research directions in this field.
Journal Article
Precise Etching of Aluminum Conductors in the Technology of Switching Devices of Microsystem Engineering
An experimentally obtained precise technology for forming a controlled profile of aluminum conductive paths with the given resistance is presented. The technology is based on anisotropic plasma-chemical etching of aluminum in a BCl3–Cl2 gas mixture, followed by precise adjustment of the track resistance using the dry plasma-chemical method. It is shown that in order to ensure the highest quality plasma-chemical etching of aluminum with minimal underetching under the photoresist mask, with the minimal slope of the aluminum conductive path profile, and the absence of defects in the etching pattern and etched areas, it is necessary to use a multistage iterative technological process with technological operations of surface preparation before etching and operations of removing the polymer and photoresist after etching.
Journal Article
The effect of different treatment protocols on shear bond strength in resin composite restoration repair
Background
It was aimed to investigate the effect of sandblasting and laser surface treatment on shear bond strength in composite restoration repair in vitro.
Methods
A micro-hybrid composite (Filtek Z250, 3 M-ESPE, USA) was used to prepare 120 samples. The samples were subjected to a thermal cycle test 5,000 times between 5 and 55
0
C, and they were randomly divided into 12 groups (
n
= 10). No surface treatment was performed in Groups 1 to 4, which were designed as control groups. The surfaces of the samples in Groups 5 to 8 were sandblasted with a Cojet device, and the surfaces of the samples in Groups 9 to 12 were applied Er, Cr: YSGG laser. After the sample surfaces were divided into groups with and without acid etching, universal adhesive was applied, and the repair process was performed using Filtek Z250 or nano-filled resin composite (Filtek Ultimate, 3 M-ESPE, USA). The thermal cycle test was repeated 5,000 times between 5 and 55
0
C on all repaired samples. The repair shear bond strength of the samples was measured using a universal testing device (Shimadzu IG-IS, Kyoto, Japan). The fracture types were evaluated by optical microscopy and scanning electron microscopy (SEM). Statistical analyses of the findings were evaluated by the Kruskal Wallis test and Mann Whitney U test at 0.05 significance degree.
Results
The highest mean shear bond strength values were obtained from the samples sandblasted with CoJet, followed by Er, Cr: YSGG laser, and the control group. It was determined that there was a significant difference between the mean shear bond strength values obtained from the control group and the other surface treatment groups (
p
< 0.05). In general, significantly higher mean shear bond strength values were obtained when the universal adhesive was applied in total-etch mode compared to the application in self-etch mode (
p
< 0.05). Additionally, it was determined that higher shear bond strength values were obtained with Filtek Ultimate compared to Filtek Z250 (
p
< 0.05).
Conclusion
Within the limitations of this study, it can be concluded that the use of universal adhesive in total-etch mode, in addition to surface treatments on the resin composite surface in the repair protocol and the use of nano-filled resin composite as repair material can increase the mean shear bond values in repair.
Journal Article
Comparative in-vivo bond failure rate of orthodontic brackets when bracket base is treated with micro-abrasive blasting vs . acid etching: eighteen month randomized control trial and scanning electron microscope study
The aim of this study was threefold. Firstly, it aimed to introduce and detail a novel method for chemically etching the bases of stainless-steel orthodontic brackets. Secondly, the study sought to investigate the structural alterations within the brackets' microstructure following chemical etching compared to those with sandblasted bases, using electron microscopy analysis. Lastly, the study aimed to evaluate and compare the long-term durability and survivability of orthodontic brackets with chemically etched bases
those with sandblasted bases, both bonded using the conventional acid etch technique with Transbond XT adhesive, over an 18-month follow-up period.
The study was a randomized clinical control trial with triple blinding and split-mouth study design and consisted of two groups. The brackets in the sandblasted group were prepared by sandblasting the intaglio surface of the base of the bracket with 50 µm SiO
particles. Hydrofluoric acid was used to roughen the base in the acid-etched group. The bases of the brackets were viewed under an electron microscope to analyze the topographical changes.
A total of 5,803 brackets (3,006 acid-etch, 2,797 sandblasted) in 310 patients were bonded, in a split-mouth design by the same operator. The patients were followed for 18 months. The failure rate of 2.59% and 2.7% was noted in an acid-etched and sandblasted group, respectively. There was a close approximation of curves in the Kaplan-Meier plot, and the survival distribution of the two groups in the log-rank (Mantel-Cox) test was insignificant; x2 = 0.062 (
value = 0.804).
Acid etching if the bases of the brackets can be used as an alternative to sandblasting furthermore acid etching can be performed on the chair side.
Journal Article
Effects of Er: YAG laser and acid etching on bond strength of clear aligner attachments to fluorotic enamel
There is a lack of research on the bonding ability of attachments to fluorosis enamel. This study evaluates Er: YAG laser-assisted acid etching as a potential optimization protocol.
Twenty healthy teeth and ninety fluorotic teeth (Thylstrup-Fejerskov Index = 4) were divided into a control group (healthy enamel + acid etching) and a fluorotic group (acid etching 30/60/90 seconds vs. Er: YAG laser + acid etching). The enamel surface was analyzed using scanning electron microscopy, and the shear bond strength (SBS) of each group (n = 10/group) was tested.
Attachments exhibited higher SBS than brackets (P < 0.01). Laser-acid etching enhanced SBS compared to acid etching alone (P < 0.01). Laser-treated surfaces exhibited predominantly mixed fracture and resin cohesion fractures, in contrast to adhesive interface fractures and mixed fractures in the acid-only groups.
Er: YAG laser (100mJ/30 Hz) with 60 seconds acid etching achieves excellent bonding for fluorotic enamel attachments, restoring adhesion to healthy enamel levels while preventing over-etching damage. This protocol shows clinical potential for bonding fluorotic enamel.
Journal Article